1. The Field of the Invention
This invention relates to optical measurement of intensity of light and, more particularly, to novel systems and methods for calibrating detectors of Raman scattering.
2. The Background Art
Optical and electronic mechanisms have been developed to generate, detect, observe, track, characterize, process, manipulate, present, and otherwise manage characteristic signals representative of materials, properties, systems, and the like. In the world of engineering, many principles of physics operate predictably, repeatably, and in accordance with the plans and schemes of those harnessing those laws of physics and engineering. Accordingly, over time, the mathematics of analysis or prediction of the performance and behavior of physical systems has been developed to a fine art and a reliable science.
The application of mechanical and electronic apparatus, as well as optical systems, radiation (e.g. radar, light, etc.), and sound (e.g. ultrasonic scanning, sonar, etc.) have proven useful in monitoring many types of systems.
In the biological sciences, instrumentation has proven extremely helpful in both diagnostics and treatments. Likewise, the field of chemistry has benefitted from technology including much instrumentation, including such devices as chromatographs, spectral analysis, and the like.
For example, systems for measurement of selected chemical compositions in biological tissue have been developed in recent years. Useful examples of such apparatus are disclosed in U.S. Pat. No. 5,873,831 issued Feb. 23, 1999 to Bernstein et al., U.S. Pat. No. 6,205,354 B1 issued Mar. 20, 2001 to Gellermann et al., and U.S. patent application Ser. No. 10/040,883 identified as Publication No. US2003/0130579A1 published Jul. 10, 2003, all incorporated herein by reference.
In general, these processes rely on a technique of resonance Raman spectroscopy to measure levels of carotenoids in similar substances and tissue. In certain embodiments, a laser light is directed onto an area of tissue of interest. A small fraction of this scattered light is scattered inelastically by a process of Raman scattering in which energy is absorbed by selected molecules of interest, and is re-radiated at a different frequency from that of the incident laser light. The Raman signal may be collected, filtered, and measured. The resulting signal may then be analyzed in order to remove elastic scattering (e.g. reflectance) of the illuminating source light, as well as background fluorescence in order to highlight the characteristic peak identified as the Raman scattering signal.
In one example, a spectrally selective system, such as a charge coupled device detects radiation (e.g. light waves, photons, etc.) according to intensity and frequency (reciprocally wavelength). Thus, the wavelengths and intensities may be processed in order to quantify the amount of irradiance occurring along a spectrum of frequencies or wavelengths.
The response to impinging, coherent light on tissues may thus be characterized by the amount of energy, the number photons, or the like arriving at a detector in response to a particular illumination source. One can imagine that such a device, if sufficiently precise might conceivably measure even down to an individual photon level of quantum variation in radiant energy response.
In order to implement such devices, a method and apparatus are needed that can reliably calibrate scanners. In operating a scanner, the electrical and electronic artifacts (e.g. errors, characteristics, anomalies, bias, and so forth) of the device in question need to be characterized in order to be factored out of measurements or calculations. Typically, the variations between any two devices produced need to be some how calibrated (e.g. measured, compensated, scaled, normalized, etc.) in order that an output by a particular device be repeatable between devices. Also, two or a hundred devices of a same design need to be able to produce the same or substantially the same value of a detected parameter when evaluating the same subject. That is, the skin of an individual scanned by two or a hundred different machines of the same design should provide substantially the same output value, within some reasonable repeatability (precision) and accuracy (reflection of true reality).
Moreover, inasmuch as conditions change, such as temperature, humidity, chemistry, physical properties, and the like, over short times and long times in some expected, unexpected, predictable, or unpredictable manner, a machine needs to be calibrated to remove its own temporal (time wise) variations in operation. That is, a method and apparatus are needed to calibrate a scanner in such a way as to factor out the vagaries of physics, chemistry, temperature, external conditions, and the like that may otherwise affect the output of a device. Thus, a method and apparatus for factory and field calibration for a bio-photonic scanner would be an advance in the art.
To the extent possible, it would be an advance in the art to establish a process for processing signals received from a scanning device, in order that the hardware not be required to any performance parameter, physical characteristic, or other control parameter associated with a scanning device. Thus, it would be an advance in the art to develop signal processing or computational processing of signal data obtained from a scanner in order to provide all the foregoing calibration benefits.
Biological materials are inherently highly variable. Moreover, the portability, degradation, etc. of a sample may be problematic. For example, how does one normalize or calibrate two different machines on two different continents scanning two different populations in order that those devices read the same.
Calibration samples taken from biological materials are inherently problematic. Biological tissues are either in vivo or not. In either event, the amount of a sample, the repeatability of a sample, the control and observable characteristics of a sample are nearly impossible to maintain when dealing with biological materials. Moreover, the replication of biological materials, organisms, tissues, or other substances is extremely difficult. Moreover, the variation in conditions cannot be precisely controlled in many circumstances. Providing identical conditions, genetics, and the like in an organism is not a practical mechanism for generating calibration samples.
Thus, what is needed is a synthetic material that can be generated, manufactured, or otherwise produced by a predictable set of standards, with some processing that can be repeatably controlled, in order to provide a sample for calibrating a scanner. That is, what is needed is a synthetic material or a system of synthetic materials that can be relied upon to produce and maintain over an extended period of time a consistent radiant response when illuminated by a scanner. Accordingly, such synthetic materials may then be used to establish calibration standards that can be transported and verified worldwide.
Moreover, even within the context of a factory, having a stable, repeatable, reproducible, easily manufactured synthetic sample that can be used to calibrate machine-to-machine variations out of the performance of those machines would be extremely valuable. Moreover, some type of field calibration apparatus and method, particularly if including a reliable synthetic material as a sample, would be a substantial advance in the art in calibrating out the day-to-day or time-to-time variations in the output of an individual scanning apparatus and associated processor.